from
The Collaborative International Dictionary of English v.0.48
spitball \spit"ball`\, spit ball \spit" ball`\, n.
1. Paper chewed, and rolled into a ball, to be thrown as a
missile; -- a childish prank.
[1913 Webster]
2. (Baseball) A pitched ball in throwing which the pitcher
grips the ball between two, or three, fingers on one side
(which is made slippery, as by saliva) and the thumb on
the other side, and delivers it so that it slips off the
fingers with the least possible friction; -- also called
{spitter}. When pitched directly overhand a spit ball
darts downward, when pitched with the arm extended
sidewise it darts down and out. The use of such a pitch is
against the rules of professional baseball. [Cant] --
{Spit baller}.
[Webster 1913 Suppl. +PJC]